Materials that are typically processed into liquid hydrocarbon fuels, such as so-called light sweet crude oil, are becoming rare. The worldwide demand for materials that may be converted into liquid fuels will increasingly be met by resources such as low quality heavy sour crude oils, coal, oil shale, and biomass. The production and conversion of each of these new resources into materials that sufficiently resemble light sweet crude oil so that they may be transported to and processed in oil refineries presents unique challenges.
For example, it is well known that there are hundreds of billions of barrels of extra heavy crude oil deposits in the western hemisphere. Surface mining techniques may be applied to recover a portion of these deposits however, to mobilize the majority of these underground deposits so that they may be recovered at the surface it is believed that thermal processes such as steam flooding, or steam assisted gravity drainage must be applied. Methods currently employed to produce steam on-site usually burn expensive natural gas and produce unacceptably large quantities of greenhouse gases. The oil from these deposits must be diluted with lighter hydrocarbons once at the surface, or thermally upgraded to become a lighter hydrocarbon in order to prevent it from returning to a semisolid state that cannot be transported by pipeline to a refinery.
Thermally upgrading the heavy crude oil in the field has been a difficult process to perform on a practical basis largely because the crude oils often contain a high percentage of heavy metals and salt that damage process equipment, and conventional processes such as coking and hydrocracking require large, complex, energy and labor intensive systems that can only be operated economically on a large scale.
It would be beneficial to provide a field upgrading system that economically generates steam for heavy crude oil mobilization from heat sources that are not completely dependent on burning hydrocarbon fuels, and therefore produce less greenhouse gases. It would also be beneficial if the field upgrading process used systems that were tolerant to relatively large quantities of heavy metals and salt. Further, it would be beneficial if those systems could be intensified to a degree that allowed the crude upgrading steps to be completed in compact, easily deployed, modular units at the wellhead, or at the pre-pipeline crude oil collection and processing point.
Biomass is another unconventional resource that seems likely to play an increasing role as a feedstock for liquid fuel production. Most sources of biomass currently used as a feedstock for liquid fuel production are derived from materials such as corn, sugar cane, soybeans, and the like. These may also be valuable food products. Consequently, use of these food products as liquid fuel feedstock may increase the cost of food to consumers. Certain aquatic strains of microalgae would provide an excellent, non-food, feedstock alternative. Salt water microalgae strains have been identified as primarily the best candidates for conversion to liquid fuels however, it is difficult and expensive to completely remove all of the salt from the harvested microalgae.
It would be particularly beneficial if the microalgae could be grown on farms in the remote regions that are currently agriculturally unproductive, using locally available brackish or salt water sources. It would also be beneficial if the microalgae feedstock could be converted into relatively stable bio-crude oil using processes that were tolerant to relatively high concentrations of salt. In addition, it would be beneficial if the process used to convert the biomass into bio-crude could also produce an easily transported source of CO2 to enhance the growth of the microalgae. It would be beneficial if the harvested product could be converted in relatively compact field processors that could be economically located near the farms in order to reduce transportation costs.
Crude oil processing equipment is usually produced currently on a one-off, custom manufactured basis. Although a compact field upgrading unit may not be particularly required for the conversion of coal or oil shale into liquid fuels, it would be beneficial if certain processing steps applied to one of these alternate resources could be universally applied to all of these alternate liquid fuel feedstock resources. Processing equipment for those universally applied steps could therefore be mass produced to reduce capital equipment costs for all of these resources.
The present invention includes four systems, namely, a system where catalyst is mixed with the feedstock prior to entering a thermal reaction zone, a system comprised of a thermal coking reaction zone where the heat is supplied to the admixed feedstock and catalyst by a flowing heat transfer medium, systems for converting the coke produced in the thermal reaction zones into gases, and systems for recovering and reusing the heat transfer medium and catalyst.
Bitumen, extra heavy sour crude oil, heavy sour crude oil, vacuum and residual bottoms are generally upgraded by processes that involve the use of thermal energy to crack long chain hydrocarbon molecules into smaller chain hydrocarbon molecules. These upgrading processes may be generally categorized as either carbon rejection processes as exemplified in U.S. Pat. No. 2,905,595 issued to Berg, or as hydrogen addition processes as exemplified in U.S. Pat. No. 4,804,459, issued to Bartholic et al, and the like. Carbon rejection processes are usually non-catalytic processes conducted at near atmospheric pressure conditions. The quality of liquid fuels produced by most carbon rejection processes are relatively unstable and require a further hydrogenation step to enhance stability. If a carbon rejection process was to be deployed in the field it would be beneficial if the quality of the liquids produced could be sufficiently stable to allow pipeline transportation without additional hydrogenation. Certain materials such as those described in U.S. Pat. No. 5,853,565, issued to Cayton are recognized coke promoters. The inventors have discovered that adding materials that are coke promoters (hereinafter referred to as coking catalysts) to a feedstock has the effect of lowering the temperature of the thermal cracking reaction and increasing the thermal cracking reaction rate. Residence time within the reactor may therefore be shorter, over-cracking is mitigated, and a higher quality, more stable liquid product is produced.
Hydrogen addition processes are usually catalytic processes conducted in a hydrogen atmosphere at high pressure. Because these systems employ hydrogen under high pressure applicant believes they are unlikely to be employed as the main thermal process for upgrading in the field. However, hydrogen addition techniques may be employed in the field in some sub-systems such as hydrotreaters without departing from the spirit of the invention. A number of hydrogen addition processes that employ mixing catalyst or catalytic material precursors with the crude oil being processed have been suggested. These processes may be exemplified by process such as those described in U.S. Pat. No. 4,769,129, issued to Barbou des Courieres et al, and the like. Hydrogen addition processes that use molten alkali metal salts to catalyze or assist the upgrading of long chain hydrocarbons such as coal or heavy crude oil may be exemplified by U.S. Pat. No. 5,954,949 issued to Ohsol et al, and U.S. Pat. No. 3,948,759 issued to King et al, and the like. A problem inherent in all these processes, amongst others, is the complete recovery of all of the catalyst they employ. The cost of catalyst consumption is often one of the factors that prohibit the practical deployment of these processes.
The primary function of the catalyst in the present catalytic coking process is to promote the formation of coke, hence the use herein of the term coking catalyst. Unlike the hydrogen addition processes described above where the main function of the catalyst is to assist hydrogen to bond with a thermally cracked hydrocarbon. Surprisingly, many of the same materials like metal sulfides, especially molybdenum sulfides, that assist hydrogenation under typical hydrogen addition conditions of pressure, temperature, and atmosphere, conversely promote the production of coke under typical carbon rejection conditions. The inventors have found that certain water soluble metal salts such as sodium molybdate and sodium vanadate are highly effective as coking catalysts at the typically low or near atmospheric pressure conditions, and at somewhat lower temperature conditions than those employed in typical carbon rejection processes. This can be important if the current invention is applied to process certain feedstocks because many of them, such as extra heavy crude oils, often contain metals such as molybdenum, vanadium, and nickel that can be readily extracted by the process of the invention and converted into coke promoting catalyst. When processing a feedstock comprised in part of compounds containing these heavy metals the inventors believe that after an initial charge of catalyst, no additional catalyst may need be added. Further it is likely that eventually more catalyst precursors will be generated than are used in the process and that they will need to be systematically withdrawn to maintain steady state production.
One of the many problems inherent in typical carbon rejection processes is that the coke produced is difficult to handle and transport from the reaction zone. Methods for using molten salts to assist in the transport of coke from the reaction zone, and to insure that coke does not build up and stick to surfaces within the reaction zone have been described in a number of patents including for example U.S. Pat. No. 2,730,488 issued to de Rosset et al, and others. These patents describe systems where the coke is mixed with a molten salt, often an alkali metal hydroxide or alkali metal carbonate to assist with transport through the reaction zone. Other processes such as the Kellogg coal gasification process as described in full in the report entitled “Commercial Potential for the Kellogg Coal Gasification Process —1967”, by Dr. George T. Skaperdas, posted at the web site http://www.fischer-tropsch.org/DOE/DOE_reports/180358/pb180358_toc.htm, disclose how molten salts may be used as both a heat transfer medium and a catalyst. The inventors have discovered that using a flowing molten salt as a heat transfer medium is beneficial, but mixing the molten salt with the hydrocarbon feedstock is ineffective as a means to inhibit coke sticking in the reaction zone, and is not desirable in the thermal cracking zone of the catalytic coking process of the present invention. Rather, the use of certain surface effects created between the heat transfer medium and the hydrocarbon feedstock are preferable.
Although it is undesirable to mix the heat transfer medium with the hydrocarbon feedstock in the thermal cracking zone of the present invention, a number of processes have been described for generating hydrogen through the catalytic reaction of a molten salt with carbon, including U.S. Pat. No. 3,387,942, issued to Habermehl et al, U.S. Pat. No. 3,252,774 issued to McMahon et al, and U.S. Pat. No. 2,517,177 issued to Carter. The use of the described processes or variation on these processes may be beneficially employed in the current invention after the catalytic coking process has been completed. U.S. Pat. No. 3,786,138 issued to Shalit et al, which is incorporated herein in its entirety by reference describes a process where carbon and water are catalyzed by a molten alkali metal salt at high temperature to produce hydrogen gas and further describes methods for recovering and reusing the alkali metal salt catalyst.
The U.S. Pat. No. 3,786,138 patent described above provides a method for recovering hydrogen gas from a catalyzed reaction between the coke and water. The process will also be particularly beneficial in certain cases, such as microalgae biomass growth and production facilities, as a CO2 absorbent is inherently produced that can be transported to a site proximate to the biomass growth area before it is induced to release its CO2 content. Due in part to the fact that insufficient steam is produced in the field by using the methods described in U.S. Pat. No. 3,786,138 (the “'138 patent”), methods to mobilize extra heavy or heavy crude oils by steam flooding or steam assisted gravity drainage or the “'138 patent” process of hydrogen production and catalyst recovery would not be generally preferred for those applications.
All carbon rejection processes produce a coke or carbon by-product that must be disposed of, burnt, sold, or partially converted into liquid fuels. Burning the coke by-product significantly increases the quantity of greenhouse gases produced by an upgrader and may be prohibited by law in many jurisdictions. Coke produced at remote locations from crude oils which are comprised in part of contaminating heavy metals are likely to be uneconomical to transport to markets that might wish to purchase them. Carbon gasification processes are described in the aforementioned Kellogg Company report by Skaperdas. Carbon gasification processes are typically combined with electrical generating systems that require complex equipment that is difficult to operate economically on a small scale. It would be beneficial if a carbon rejection process used in a field upgrader could be economically operated on a relatively small scale, and if all of the carbon rejected in the process could be converted into useful gases such as hydrogen and carbon monoxide.
One method for accomplishing the conversion of coke into useful gases that lends itself to modular construction techniques and ties in with byproducts of the inventors' catalytic coking process is the carbothermic reduction of the molten alkali metal salt with coke. The carbothermic reduction of alkali metals is a well known metallurgical process, and is described in a number of patents including U.S. Pat. No. 2,774,663 issued to Kirk, U.S. Pat. No. 2,930,689 issued to McGriff, and U.S. Pat. No. 3,971,653 issued to Cochran. When sodium hydroxide is used as the molten alkali metal salt heat transfer medium in the catalytic coking process of the present invention, the carbothermic reduction of the molten alkali metal hydroxide by the coke produces gases comprised in part of carbon monoxide, hydrogen, and sodium metal vapor.
Recovery of the sodium hydroxide heat transfer material can be accomplished by adding water in a controlled manner to react with the sodium vapor and release additional hydrogen gas. Carbon monoxide and hydrogen may be combined in the presence of a catalyst in well defined processes such as the Fisher-Tropsch process to form liquid fuels. The intensely exothermic reaction between sodium vapor and water has the additional benefit of providing significant quantities of high quality steam, without the production of greenhouse gases, which may be used in many field applications, such as for example, steam flooding, steam assisted gravity drainage, electricity production, and the like.